This invention relates to coating compositions comprising hydroxy functional film former and a novel flow control additive which improves the flowout characteristics of the coating composition, increasing both smoothness and evenness of the coating film. The compositions are particularly well suited for automotive applications wherein the coating composition includes metallic pigment. More particularly, the invention relates to such coating compositions wherein the novel flow control additive is a stable crosslinked dispersion prepared by addition polymerization of (a) first and second ethylenically unsaturated monomers each bearing functionality capable of crosslinking with the other and (b) at least one other monoethylenically unsaturated monomer, in the presence of (I) organic liquid which is a solvent for the polymerizable monomers, but a non-solvent for the resultant polymer and (II) a particular polymeric dispersion stabilizer which bears pendent ethylenic unsaturation capable of reacting with monomers employed in the addition polymerization. Still more particularly, the invention relates to such compositions including the stable crosslinked dispersions wherein the polymeric dispersion stabilizer comprises a random copolymer segment of ethylenically unsaturated monomers, some of which are characterized in that homopolymers thereof would be substantially insoluble in the organic liquid used to form the stable dispersion and some of which are characterized in that homopolymers thereof would be substantially soluble in the organic liquid used to form the stable dispersion. Preferred compositions including the stable crosslinked dispersions are intermediate and high solids thermosetting compositions which are adapted to provide an automotive topcoat demonstrating hardness, high gloss, outstanding durability and excellent resistance to solvents and water.
Because of increasingly strict solvent emission regulations in recent years, low solvent emission paints have become desirable. A number of intermediate and high solids paint compositions have been proposed to meet these low solvent emission requirements. However, many of these compositions are deficient because of difficulty in application, poor flow out, lack of smoothness and evenness and poor distribution of pigment, particularly metallic flake pigments. The deficiency in compositions including metallic flake results from undesired reorientation of the metallic flake during application and curing of the coating. Flake reorientation results primarily because of the very low viscosity resins used in paint compositions to accommodate intermediate and high solids. The viscosity of these resins is not sufficient to immobilize the flakes which tend to redistribute themselves to show "reverse flop" and non-uniform distribution.
The preferred coating compositions of this invention, as a result of the improved flow control additive component thereof, combine desirable properties, including lower solvent content and low application viscosity, while also overcoming deficiencies of some of the previously proposed intermediate and high solids materials, thereby achieving intermediate and high solids coating compositions particularly adapted for automotive topcoats and still more particularly adapted for automotive topcoats including metallic flake as pigment.
Concurrently filed application Ser. No. 292,963 entitled "Polymeric Dispersion Stabilizer and Stable Dispersion Prepared Therefrom" assigned to the assignee of this application claims stable crosslinked dispersions employed as flow control additives in compositions of this invention. This concurrently filed application is a continuation-in-part of Ser. Nos. 199,874 and 199,396 filed Oct. 23, 1980.
Compositions of the type disclosed and claimed in this application, except for the addition of the stable crosslinked dispersion flow control additive, were developed by coworkers of the inventor of the subject invention prior to the invention described and claimed herein. These compositions were prepared both with and without flow control additives. However, the preferable compositions were those prepared using a flow control additive which was made generally in accordance with the teaching of U.S. Pat. No. 4,147,688 to Makhlouf et al. That patent teaches stable crosslinked dispersions wherein crosslinked acrylic polymer microgel particles are formed by free radical addition polymerization of alpha, beta ethylenically unsaturated monocarboxylic acid, at least one other copolymerizable monoethylenically unsaturated monomer and a certain percentage of crosslinking monomer, in the presence of a hydrocarbon dispersing liquid (see abstract, examples and claims). Other crosslinked dispersions containing microgel particles are disclosed in the patent applications and patents referred to in the Makhlouf et al disclosure.
U.S. Pat. No. 4,025,474 to Porter et al discloses a polyester based coating composition which includes the crosslinked dispersions disclosed by Mahklouf et al. U.S. Pat. No. 4,074,141 to Porter et al disclose carboxylic acid amide interpolymer--based coating compositions including the same crosslinked dispersions. U.S. Pat. No. 4,115,472, also to Porter et al, discloses urethane coating compositions also including the crosslinked dispersions of Mahklouf et al. U.S. Pat. No. 4,055,607 to Sullivan et al discloses thermosetting compositions of (a) solution acrylic polymer, (b) at least 0.5% of microgel particles formed by polymerizing hydroxyl bearing monomers with nonhydroxyl bearing monomers in the presence of the stabilizer disclosed by Mahklouf et al, and (c) melamine resin. The microgel dispersion of Sullivan et al thus contains functionality capable of reacting with the melamine crosslinking agent.
All of the stable crosslinked dispersions referred to above contain microgel particles and are of the dispersion type generally referred to in the art as nonaqueous dispersions. These nonaqueous dispersions have been developed in recent years in attempts to improve the efficiency of applying protective or decorative coatings to a variety of objects and have been particularly widely used in the coating of motor vehicle bodies and vehicle components. Those skilled in the art will be aware of numerous prior art references relating to nonaqueous dispersion technology. Among the more pertinent prior art references, insofar as this invention is concerned, in addition to the Makhlouf et al patent and the patents referred to therein, are those which have taught various improved stabilizers and methods of making the same. These include: U.S. Pat. Nos. 3,317,635 to Osmond et al; 3,514,500 to Osmond et al; 3,607,821 to Clarke; and 3,814,720 and 3,814,721, both to Maker et al.
U.S. Pat. No. 3,317,634 to Osmond et al teaches nonaqueous dispersions stabilized by block or graft copolymers of ethylenically unsaturated monomers with a precursor containing a polymeric chain and an unsaturated group with which the monomer polymerizes in vinyl-type manner to produce a polymeric vinyl chain of a different degree of polarity from the original polymeric chain (Col. 2, lines 1-9). Stable dispersions of synthetic monomers in organic liquids may be made in accordance with Osmond et al by precipitating the polymer in the organic liquid in the presence of the stabilizer such that one polymeric chain is solvated by the organic liquid and another is non-solvated and consequently becomes associated with the non-solvated polymer (Col. 2, lines 50-56).
U.S. Pat. No. 3,514,500 to Osmond et al teaches a stabilizer for nonaqueous dispersions, which stabilizer comprises a polymeric backbone and attached thereto at least five side chains of different polarity than the backbone (See abstract). The side chains are attached to the backbone by a condensation reaction between side chains containing only one reactive group per molecule and a backbone containing at least five complementary reactive groups per molecule (Col. 1, line 71-Col. 2, line 1).
U.S. Pat. No. 3,607,821 to Clarke teaches a stabilizer for nonaqueous dispersions wherein the stabilizer is chemically reacted with dispersed particles of the dispersion (Col. 1, lines 36-42). Each co-reacted stabilizer molecule forms from 1 to 10 (preferably 1 to 4) covalent links with the dispersed polymer (Col, 1, lines 50-52). The covalent links between the stabilizer and the dispersed polymer are formed by reaction between chemical groups provided by the stabilizer and complementary chemical groups provided by the dispersed polymer or by copolymerization reaction (Col. 1, lines 63-67).
U.S. Pat. No. 3,814,720 assigned to Ford Motor Company, the assignee of this application, teaches nonaqueous dispersions which employ a methylolated addition copolymer of an ethenic monomer and an amide of an unsaturated acid (see abstract and claims).
U.S. Pat. No. 3,814,721, also to Maker et al and also assigned to Ford Motor Company, teaches nonaqueous dispersions which are prepared employing a precursor addition copolymer which is prepared by reacting an active ethenic monomer having a functional epoxy, hydroxy, cyanato, or carboxy group with another active ethenic monomer free of functional groups in an aromatic or alcoholic solvent, followed by addition of an aliphatic liquid in which the polymer is insoluble, followed still further by the addition of a third ethenic monomer having one of such functional groups and a forth ethenic monomer free of such functional groups, such that the aliphatic liquid is a non-solvent for the second addition copolymer which is dispersed throughout the medium (see abstract, examples and claims).